(1) Field of the Invention
A mask and a method of forming a mask having a binary mask pattern and an attenuating phase shifting mask pattern on the same mask substrate.
(2) Description of the Related Art
Attenuating phase shifting masks are often used to form features such as contact holes in situations where critical dimensions are very small. Problems such as side lobe effect can occur in situations where small contact holes and larger contact holes are required on the same integrated circuit layer. FIG. 1 shows a top view and FIG. 2 a cross section view of a conventional attenuating phase shifting mask having small holes 16 and larger holes 18 on the same mask substrate 20. Since the attenuating phase shifting material 22 attenuates the light but does not block the light totally the intensity required for satisfactory results in the region of the mask having small holes can cause side lobe effect problems, unwanted light at the pattern edges, in the region of the mask having larger holes.
One conventional method of handling the problem of two sizes of contact holes is to use two masks, an attenuating phase shifting mask for the small holes and a binary mask for the larger holes. The two mask method works well but has the problem of reduced throughput and increased cost.
U.S. Pat. No. 5,429,897 to Yoshioka et al. describes the use of an attenuating phase shifting pattern and an attenuating type auxiliary phase shifting pattern to prevent exposure of the region around a normal exposure region.
U.S. Pat. No. 5,527,645 to Pati et al. describes a method of producing phase shifting photolithographic masks. The method includes the steps of defining a binary image pattern to be formed by the illumination system on the image plane, generating a continuous mask function of continuously varying phase which satisfies predetermined error criteria based on the transmission function and the binary image pattern.
U.S. Pat. No. 5,474,865 to Vasudev describes a globally planarized mask using embedded absorbers.
U.S. Pat. No. 5,326,659 to Liu et al. describes a method of forming a mask which compensates for optical diffraction, provides for an extended depth of focus, and allows a shift of the focus plane.
U.S. Pat. No. 5,468,578 to Rolfson describes a method of forming phase shifting masks which avoids the problems of phase conflict areas.
A Patent Application (TSMC-97-201) entitled "A NEW DOUBLE LAYER METHOD FOR FABRICATING A RIM TYPE ATTENUATING PHASE SHIFTING MASK", Ser. No. 08/956,971, filed on Oct. 23, 1997, and assigned to the same assignee describes a method of forming multiple patterns in a single layer of resist. The method uses two different electron beam exposure doses followed by dry anisotropic etching to transfer a pattern from the top part of the resist layer to the bottom part of the resist layer.
This invention relates to an attenuating phase shifting mask and method of forming the mask which can be used to form contact holes of different sizes on the same mask substrate while avoiding the problems of side lobe effect.